There are two ways to define colors, CMY and RGB. CMY stands for Cyan, Magenta, and Yellow. Mixing cyan, magenta, and yellow can be compared to blending paint. When cyan, magenta, and yellow are amalgamated together, the result is black. CMY is sometimes known as CMYK, which stands for Cyan, Magenta, Yellow and black (so as not to be confused with Blue). These colors are sometimes called process colors, because you use them in four-color printing. If you have a typical full color printer, the inks used consist of these primary colors. The term “primary colors” mean that mixing these colors together can create all colors. Cyan, magenta and yellow are theoretically all one needs, but to save costly color inks many printers also have a black cartridge. The CMY color model is called a subtractive color model, because the process ink pigments “subtracts” or absorbs certain colors and reflects others.
RGB stands for red, green, and blue. Mixing red, green, and blue together can be compared to blending light beams. When the lights off, everything looks black. If all the lights are on, the result is white. The RGB model is used in a television or computer monitor. The colored spots of a TV screen emit three colors, and the sum of these colors determines the color you see. This is called an additive color model. Each color in the RGB system has a value for the amount of Red, Green and Blue in each picture element (pixel). In the internal Microsoft® Windows® image descriptions, this value goes from 0 to 255, where 0 for all three colors equals black, and 255 for all three colors equals white. This means that one can get more than 16 million different colors (TrueColor) because 256*256*256=16,777,216, but one can only get 256 shades of gray.
A full color printer forms the various colors of an image by mixing inks of different colors on the paper. That is, a full color printer uses the CMY or CMYK color system. The amount of each color determines the hue. Typically the paper is white and no ink produces a white dot. Mixing yellow and cyan produces a red dot and mixing cyan, magenta, and yellow in equal amounts produces a black or gray dot.
Hue describes what shade of color a particular color is, such as red, orange, indigo, or green. As in the rainbow, the starting and ending color is red. Hue can be described as a color circle with red at 0 degrees, yellow at 60 degrees clockwise, continuing with green, cyan, blue, magenta, and red again at 360 degrees. Saturation is a term used with how bright the color is.
There are a number of different types of printers commercially available, but not all types are suited to be POS printers. POS printers are used to print cash register receipts or credit card charge statements. Full color printing is not required, nor is the ability to print on different types of paper. POS printers tend to be compact so as not to clutter up a cashier's work area.
Many types of POS single color printers are commercially available. Dot matrix printers, thermal printers, and ink jet printers are all used because of their speed and reliability. POS color printers are rare in the marketplace. POS dot matrix color printers require a multi-colored ribbon, which adds to the complexity and size of the printer. Color thermal printers are under development, but it is hard to do color graphics on a thermal printer. In addition, special paper is required. Color ink jet printers are unsuitable for POS printers because adding three additional ink jet cartridges for full color (also known as 4-color, i.e., three colors plus black) would add width and complexity to the printer.
A two-color printer typically makes one pass with the primary color followed by one pass with the alternate color. This is normally because of the time it takes to process and send the printer commands to the printer. In some cases, especially with technologically older inks, two passes are required to ensure that one color dries before the second color is printed.